1. Field of the Invention
The present invention relates to a screen printer for screen printing. Particularly, the present invention relates to the screen printer which does not result in uneven printing.
2. Background Art
The drawing of FIG. 7 illustrates a perspective side view of the actual screen printer.
The drawing of FIG. 8 outlines a lateral view of the screen printer.
The drawing of FIG. 9 outlines a plane view of the screen printer.
FIG. 7 illustrates the following elements: a screen printer 101; a base 102 of the screen printer; a movable table 103 attached to allow for a movement; a guide rail 104 for guiding the movement of movable table 103; an operating box 105 of the screen printer; an operating switch 107 attached to the operating box; and a printing unit 109 for printing a work placed on the movable table 103.
FIGS. 8 and 9 illustrate the following elements: a work 110 placed on top of the movable table 103; a screen plate 200; a screen frame 201 of the screen plate 200; a screen 211 affixed to the screen plate 200; a slider 106 holding a squeegee 111 and a scrapper (not illustrated), for sliding in directions indicated by arrows A and D; and frames 108 for sliding the slider 106.
The movable table 103 is situated on the guide rail 104 which is laid to the base 102 so that the movable table 103 can move along the guide rail 104, sliding from side to side. When the movable table 103 moves beneath the printing unit 109, the movable table 103 is stopped by a stopper which is not illustrated, and then the printing unit 109 performs a screen print on the work 110.
Suction holes 190 are installed to the movable table 103. The work 110 is stuck to the movable table 103 by sucking up the air through the suction holes 190 as indicated by the arrows.
The drawing of FIG. 10 illustrates printing states of the printing unit 109.
An ink 51 is applied uniformly on top of the screen 211.
In FIG. 10, state (a) illustrates a state before commencing the printing. There is a distance 95 between the screen 211 and the work 110. In FIG. 10, state (b) illustrates a case of starting the printing by applying a pressure P to the squeegee 111. In FIG. 10, state (c) illustrates a case of printing a pattern 52, pattern 53 and pattern 54 onto the work 110 in accordance to pre-made patterns of the screen 211. In FIG. 10, state (d) illustrates completion of the printing. During the states (b) to (d) of FIG. 10 which illustrate printing in progress, the pressure P applied to the squeegee 111 is constant as illustrated in graph (e) of FIG. 10.
While printing as shown in FIG. 10, there is a case when a height H1 of the pattern 52 and a height H2 of the pattern 54 illustrated in state (d) of FIG. 10 may become different. Although the screen 211 is firmly affixed to the screen frame 201, a tension varies in different places of the screen 211. Therefore, even if a constant pressure P is applied from above to down, the printed heights of the patterns may vary depending on the position printed, or in other words, the heights of printed ink may become different. There is a problem of unevenness in the spread of the ink on the work 110 or a problem of uneven printing.
The drawing of FIG. 11 illustrates a method to resolve the previously described unevenness in the spread of the ink.
When the printing is in progress, a lifting apparatus (screen detaching apparatus) not illustrated is used to lift the screen plate 200 in a direction of arrow X (H10&lt;H20&lt;H30). By lifting the screen plate 200 from a side where the screen printing is finished, the conventional screen printer offsets a change in the tension on different positions of the screen 211. As a result of this, the height H1 of pattern 52 printed at the edge of the work 110 and the height H2 of pattern 54 printed at the center of the work 110 can be made almost equal.
However, by using this method of lifting one side of the screen plate 200 as illustrated in FIG. 11, a pressure is applied to the screen plate 200 more than necessary. Due to this, a position of printing the pattern installed to the screen 211 may be displaced, and a durability of the screen plate 200 may be reduced.
The present invention attempts to solve the problems mentioned above by aiming to achieve a screen printing for even printing to the work 110 without having to use the lifting apparatus.